I'm a early 30s Soldier who trains MMA afterwork and quite frankly I'm not exactly "all there" due to fatigue.

Has anyone used an energy supplement for practice? Suggestions?

Do not use anything like Red Bull. Not in anyway good for ya and doesn't help what so ever in terms of boosting T-levels, which are of course vital for training. Your best bet is using some kind of pre-workout shake. Creatine is also advisable. It'll give you that little bit more energy needed for your work out. In general I'd say stay as natural as possible and as Voiceless said. Sleep is very important.